My new Scratch Build

I did not really mean to but I ended up building a new version of a rocket I designed a lot of years back. The old version flew so well I used it to teach composite classes. There is a lot of history to the old version and why I designed it but this thread is about the one I just did.

This one is 49" total with a custom carbon body tube. As it sits it is roughly 7oz and runs on 24mm motors. I rolled the tube using some Uni Carbon cloth a had with a fiberglass layers for hoop strength. The fins are glassed .125" ply and they are slotted so they mount to the motor tube. The BT is turned from HL60 foam and fiberglassed. The NC is turned from balsa and it was hardened with CA and then fiberglassed. It has an internal baffle that also works as the shock cord mount. It is fiberglassed plywood.

I plan to build a micro rail pad so it will be getting the micro buttons.

I have not run any simulations but I believe that on a F39 she will get up and go.

I am working on a dual deployment system that will not require an avionics bay.

I am already designing a larger version for a 38mm motor.

Yup, My wife lets me build in the house....

Quite a workshop you got! Oh nice rocket....

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Very nice, what is the diameter? Do you have any tips or photos of the carbon body tube rolling?

My "real shop" is a cluttered mess right now so she is being quite tolerant. If I need to use my vacuum system or my larger curing oven I have to head to the garage/shop. I still do all my turning and other machining out there. At some point I need to get it in working order so I can get back to teaching composite methods. I also have some larger projects in mind.

As for rolling carbon or fiberglass tubes....I have been doing it for over 20 years in one form or another. Tapered tubes are super simple as they release from the mandrel quite easily. I have actually been thinking about writing a book on doing all this stuff.

A basic run down is as follows. Use a good resin that has a decent working time. I have used Resin Research for the last 15 years. Have everything laid out and planned. The two things that will fight you are the release from the mandrel and the surface finish. In order to get a nice surface finish and the best mechanical properties you need an out wrap that will apply pressure. The flip side is this makes getting the mandrel out more difficult. I have developed a couple of different systems and each has it's place. For tapered tubes like airplane fuselages I use a mylar tape wound on the mandrel. For a straight mandrel like this rocket I use parchment paper.

The very best way to start is to build glass tubes over paper tubes. This can be almost any tube that is stiff enough for you wrap on. I taught a class one weekend to my club and we wrapped 2" mailing tubes to build the WISHB I designed a bunch of years back. Once the glass is cured you could soak the paper tube out if you wanted to with water.

I will attach a pic of a 2" WISHB it is a 2" mailing tube that has been fiberglassed.

This rocket is 43mm OD

Understanding resins are thermogenic, I've wondered about forming composites around a casting wax dowel and later heating to loosen the wax. Do you find vacuum forming preferable over compression molding (inflating against a rigid tube) or is it six of one, half dozen of another? Its taken two years but we're finally getting some interest in the school house to make things happen and the tools to do it with.

I have not played with the waxes.

I find vacuum bagging and inflation bladder molding each have their place. For doing "flat" surfaces like glider wings and fins I prefer either bagging or a system i developed of bagging into a mold. For tube type structures there are really two methods I use.

If it is a simple tube I do a "jelly roll" of alternating layers of two or more materials. I adhere my layers with 3M77 and then roll on a mandrel and then do a compression wrap with a mylar tape to remove as much resin as possible. I have gotten down to a 60% cloth lay-up a couple of times. This is considered by many to be the ideal ratio. A 50-50 ratio also works perfectly fine and unless we are looking for world class performance chasing grams is not worth the trouble.

If it is a more complicated shape like a fuselage I use a very stout mold with an inflated bladder. I have run bladders up to 60psi but I do not see results that justify going that high. Forty psi is normally enough to get very good results.

For my rocket tubes I like PVC pipe. I have adapted a few tips from stuff I have seen on the net. I now sand the pipe lengthwise to reduce surface tension/friction. I do a base layer of parchment paper. That stuff is super slick. I have not found a tape that will really stick to it. Basic scotch tape sticks enough to roll a tube over it.

I have a lathe I built from a 1/2" drill. I drill holes in the center end caps for the pipe. I mount up mandrel/tube in the drill but I don't tighten the chuck down just yet. I can now wet out and roll my cloth onto the tube quite easily.

Once I have the cloth all wound on the tube I lock down the chuck and start the drill so it slowly turns the tube. I can now use my paint roller to smooth out the cloth and make sure it is all wetted out. Once I am happy with that I speed the drill up just a bit so I can apply a heavier load and it will keep spinning. Now I do an over wrap of mylar tape so the wraps over lap by 50%. You will start to see blobs of resin showing on top of the tape.

My curing oven has a fan for circulating air inside the oven so I can simply lay the tube in the oven. If the air does not circulate in your curing oven I suggest you rotate the tube so it does not warp. I do recommend some kind of curing oven. Many resins will do okay curing at room temps but really do not real their full mechanical values until they are cured at 100 degrees F or higher. I tend to cure at 150 deg as it works well with my resin of choice.

One the tube is cured I let it get down to room temp before I do any more. Once there I pull once of the caps and fill the tube with ice. I now add water or salt water. This step causes the PVC to contract making the removal of the new composite tube quite manageable.

The mylar tape should simply unwrap without a lot of trouble. For mylar tape I use old VHS cassette tapes but i am sure there are other options. I may try some plastic tape like "caution tape" as VHS tapes are getting harder to find. I had to fight a spider that was hiding behind the last batch I found on a shelf.